nubie +problem 747

hello all one oap joining in.
problem. switch on fsx gold 747 to fly. great no problem.choose another a/c to fly all ok.
return to 747 big fat sausage,when viewed from rear a/c in two halves.shut down select another a/c all ok back to 747 sausage.
any help would keep an old chap flying.?
shut down come back say in half an hour ok